Thursday, February 10, 2011

Thurs-Demo: The one with Corn Syrup

This week's demo is all about particles falling through viscous fluid. In this case, we'll be dropping some steel ball bearings into corn syrup.

What a Drag! Falling Through Syrup from Matt Kuchta on Vimeo.

The fluid behavior in the video is mostly laminar - the size of the sphere and viscosity of the fluid don't produce any separation of the flow or turbulence. I wrote a bit about Stoke's Law in a previous post. For particles falling through water, the maximum particle size that will exhibit laminar behavior is around 0.1mm. For the steel spheres, we didn't manage to see any flow separation - but did see interference with the container's edge with really big spheres.

A graph of the resulting velocity shows a nice linear relationship between the square of the sphere's radius and its terminal velocity (except for the largest spheres, where interference with the container's edge slowed them down.


  1. How would a snail crawl thru a viscous fluid?

  2. Aydin,
    It depends. The morphology of the foot and the properties of its "slime" may help it move around. Some of these aquatic and littoral species that graze through algal mats may have interesting ways of propelling themselves through stuff.

    I've been thinking I should do some hydrodynamics of snail shells soon. Perhaps dropping shells through corn syrup would be entertaining.

  3. When the snails are very small, surface tension also comes into play. I have seen very small snails remove themselves from drops of water with great difficulty.